The ‘godzilla’ weather phenomenon El Niño in 2015-16 has been blamed for the worldwide surge in cases of killer viruses.
The natural occurrence, caused by warm water shifting in the Pacific ocean, changes weather conditions across the planet. The one that struck three years ago is the strongest on record.
During the 2015-2016 event, the precipitation levels and vegetation created the perfect conditions for dengue fever, cholera and the plague to spread, researchers have said.
It had devastating effects throughout the world, including causing a spike in infections in Colorado, New Mexico, Tanzania, Brazil and Southeast Asia.
The research is believed to be the first study, by NASA, to assess the public health impacts of the major climate event on a global scale.
Experts believe it could serve as a ‘remarkable tool’ to save lives in the future, building on existing models that predict outbreaks.
The ‘godzilla’ weather phenomenon El Niño has been blamed for the worldwide surge in cases of killer viruses including the spread of hantavirus and the plague in Colorado and New Mexico, cholera in Tanzania and dengue fever in Brazil and SE Asia
El Niño, along with its little sister La Niña, are part of a recurring shift in climate that occurs as warm water shifts from one side of the Pacific to the other.
It is caused by a shift in the distribution of warm water in the Pacific Ocean around the equator.
The 2015–16 El Niño was ‘record-breaking’ and one of the three strongest events since 1950.
‘The impact on weather and therefore diseases in these regions was especially pronounced,’ said Assaf Anyamba, a research scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who was lead author of the study.
The study, published in the journal Nature Scientific Reports, used a number of climate datasets and public health records to quantify a relationship between disease outbreak and El Niño.
Reported cases of plague in Colorado and New Mexico were at their highest in 2015, while the number of hantavirus cases reached their peak in 2016.
Hantaviruses are a family of viruses spread mainly by rodents through urine and feces and plague is usually found in small mammals and their fleas.
According to the study, the spike in both potentially fatal diseases was an El Niño-driven increase in rainfall and milder temperatures over the American Southwest.
This spurred vegetative growth, providing more food for rodents that carry hantavirus who are in frequent contact with humans.
As their rodent hosts proliferated, so did plague-carrying fleas.
A continent away, in East Africa’s Tanzania, the number of reported cases for cholera in 2015 and 2016 soared to record numbers since 2000.
Cholera is a potentially deadly bacterial infection of the small intestine that spreads through fecal contamination of food and water.
Increased rainfall in East Africa during the El Niño allowed for sewage to contaminate local water sources, such as untreated drinking water.
‘Cholera doesn’t flush out of the system quickly,’ Anyamba said, ‘so even though it was amplified in 2015-2016, it actually continued into 2017 and 2018. We’re talking about a long-tailed, lasting peak.’
In Brazil and Southeast Asia, during the El Niño dengue fever proliferated. In Brazil the number of reported cases for the potentially deadly mosquito-borne disease in 2015 was the highest from 2000 to 2017.
In Southeast Asia, namely Indonesia and Thailand, the number of reported cases, while relatively low for an El Niño year, was still higher than in neutral years.
In both regions, the El Niño produced higher than normal land surface temperatures and therefore drier habitats, which drew mosquitoes into populated, urban areas containing the open water needed for laying eggs.
As the air warmed, mosquitoes also grew hungrier and reached sexual maturity more quickly, resulting in an increase in mosquito bites.
The findings highlight the importance of existing seasonal forecasts, said Anyamba, who has been involved with such work for the past 20 years.
Organisations can use early warnings in countries where these outbreaks occur to take preventive measures.
Based on current forecast models, the US Department of Defense does pre-deployment planning, and the US Department of Agriculture (USDA) takes measures to ensure the safety of imported goods.
Co-author Kenneth Linthicum, USDA center director at an entomology laboratory in Gainesville, Florida said: ‘Knowledge of the linkages between El Niño events and these important human and animal diseases generated by this study is critical to disease control and prevention, which will also mitigate globalization.’
He noted these data were used in 2016 to avert a Rift Valley fever outbreak in East Africa.
‘By vaccinating livestock, they likely prevented thousands of human cases and animal deaths,’ he said.
Co-author William Karesh, executive vice president for New York City-based public health and environmental nonprofit EcoHealth Alliance, said: ‘This is a remarkable tool to help people prepare for impending disease events and take steps to prevent them.
‘Vaccinations for humans and livestock, pest control programs, removing excess stagnant water – those are some actions that countries can take to minimize the impacts.
‘But for many countries, in particular the agriculture sectors in Africa and Asia, these climate-weather forecasts are a new tool for them, so it may take time and dedicated resources for these kinds of practices to become more utilized.’
According to Anyamba, the major benefit of these seasonal forecasts is additional time between the weather event and outbreaks.
He said: ‘A lot of diseases, particularly mosquito-borne epidemics, have a lag time of two to three months following these weather changes. So seasonal forecasting is actually very good, and the fact that they are updated every month means we can track conditions in different locations and prepare accordingly. It has the power to save lives.’
It has previously been suggested that El Niño sparked the plague epidemic in Madagascar, which infected 2417 people and killed 209.